Add go-ts-mode and go-mod-ts-mode (Bug#60025)

* admin/notes/tree-sitter/build-module/batch.sh:
* admin/notes/tree-sitter/build-module/build.sh: Add go-mod support.
* etc/NEWS: Mention them.
* lisp/progmodes/eglot.el (eglot-server-programs): Add them.
* lisp/progmodes/go-ts-mode.el: New major modes with
tree-sitter support.

5 files changed, 370 insertions, 1 deletions

diff --git a/admin/notes/tree-sitter/build-module/batch.sh b/admin/notes/tree-sitter/build-module/batch.sh
index e7ef45cf57d..c50b9df37ed 100755
--- a/admin/notes/tree-sitter/build-module/batch.sh
+++ b/admin/notes/tree-sitter/build-module/batch.sh
@@ -9,6 +9,7 @@ languages=(
     'c-sharp'
     'dockerfile'
     'go'
+    'go-mod'
     'html'
     'javascript'
     'json'
diff --git a/admin/notes/tree-sitter/build-module/build.sh b/admin/notes/tree-sitter/build-module/build.sh
index 4195ea58c3c..b6c83ea9b99 100755
--- a/admin/notes/tree-sitter/build-module/build.sh
+++ b/admin/notes/tree-sitter/build-module/build.sh
@@ -26,6 +26,11 @@ case "${lang}" in
     "cmake")
         org="uyha"
         ;;
+    "go-mod")
+        # The parser is called "gomod".
+        lang="gomod"
+        org="camdencheek"
+        ;;
     "typescript")
         sourcedir="tree-sitter-typescript/typescript/src"
         grammardir="tree-sitter-typescript/typescript"
diff --git a/etc/NEWS b/etc/NEWS
index 701e414fdbb..dd11b3c2715 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -3081,6 +3081,14 @@ A major mode based on the tree-sitter library for editing files
 written in TOML, a format for writing configuration files.  It is
 auto-enabled for files with the ".toml" extension.
 
+*** New major mode 'go-ts-mode'.
+A major mode based on the tree-sitter library for editing programs in
+the Go language.  It is auto-enabled for files with the ".go" extension.
+
+*** New major mode 'go-mod-ts-mode'.
+A major mode based on the tree-sitter library for editing "go.mod"
+files.  It is auto-enabled for files which are named "go.mod".
+
 
 * Incompatible Lisp Changes in Emacs 29.1
 
diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 9c5a361df7b..02bb6bb665d 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -211,7 +211,8 @@ chosen (interactively or automatically)."
                                 (elm-mode . ("elm-language-server"))
                                 (mint-mode . ("mint" "ls"))
                                 (kotlin-mode . ("kotlin-language-server"))
-                                ((go-mode go-dot-mod-mode go-dot-work-mode) . ("gopls"))
+                                ((go-mode go-dot-mod-mode go-dot-work-mode go-ts-mode go-mod-ts-mode)
+                                 . ("gopls"))
                                 ((R-mode ess-r-mode) . ("R" "--slave" "-e"
                                                         "languageserver::run()"))
                                 ((java-mode java-ts-mode) . ("jdtls"))
diff --git a/lisp/progmodes/go-ts-mode.el b/lisp/progmodes/go-ts-mode.el
new file mode 100644
index 00000000000..124d9b044a2
--- /dev/null
+++ b/lisp/progmodes/go-ts-mode.el
@@ -0,0 +1,354 @@
+;;; go-ts-mode.el --- tree-sitter support for Go  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2022 Free Software Foundation, Inc.
+
+;; Author     : Randy Taylor <dev@rjt.dev>
+;; Maintainer : Randy Taylor <dev@rjt.dev>
+;; Created    : December 2022
+;; Keywords   : go languages tree-sitter
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+
+;;; Code:
+
+(require 'treesit)
+(eval-when-compile (require 'rx))
+
+(declare-function treesit-parser-create "treesit.c")
+(declare-function treesit-induce-sparse-tree "treesit.c")
+(declare-function treesit-node-child "treesit.c")
+(declare-function treesit-node-child-by-field-name "treesit.c")
+(declare-function treesit-node-start "treesit.c")
+(declare-function treesit-node-type "treesit.c")
+
+(defcustom go-ts-mode-indent-offset 4
+  "Number of spaces for each indentation step in `go-ts-mode'."
+  :version "29.1"
+  :type 'integer
+  :safe 'integerp
+  :group 'go)
+
+(defvar go-ts-mode--syntax-table
+  (let ((table (make-syntax-table)))
+    (modify-syntax-entry ?+   "."      table)
+    (modify-syntax-entry ?-   "."      table)
+    (modify-syntax-entry ?=   "."      table)
+    (modify-syntax-entry ?%   "."      table)
+    (modify-syntax-entry ?&   "."      table)
+    (modify-syntax-entry ?|   "."      table)
+    (modify-syntax-entry ?^   "."      table)
+    (modify-syntax-entry ?!   "."      table)
+    (modify-syntax-entry ?<   "."      table)
+    (modify-syntax-entry ?>   "."      table)
+    (modify-syntax-entry ?\\  "\\"     table)
+    (modify-syntax-entry ?/   ". 124b" table)
+    (modify-syntax-entry ?*   ". 23"   table)
+    (modify-syntax-entry ?\n  "> b"    table)
+    table)
+  "Syntax table for `go-ts-mode'.")
+
+(defvar go-ts-mode--indent-rules
+  `((go
+     ((node-is ")") parent-bol 0)
+     ((node-is "]") parent-bol 0)
+     ((node-is "}") parent-bol 0)
+     ((node-is "labeled_statement") no-indent)
+     ((parent-is "argument_list") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "block") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "const_declaration") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "default_case") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "expression_case") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "expression_switch_statement") parent-bol 0)
+     ((parent-is "field_declaration_list") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "import_spec_list") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "labeled_statement") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "literal_value") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "type_spec") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "var_declaration") parent-bol go-ts-mode-indent-offset)
+     (no-node parent-bol 0)))
+  "Tree-sitter indent rules for `go-ts-mode'.")
+
+(defvar go-ts-mode--keywords
+  '("break" "case" "chan" "const" "continue" "default" "defer" "else"
+    "fallthrough" "for" "func" "go" "goto" "if" "import" "interface" "map"
+    "package" "range" "return" "select" "struct" "switch" "type" "var")
+  "Go keywords for tree-sitter font-locking.")
+
+(defvar go-ts-mode--operators
+  '("+" "&" "+=" "&=" "&&" "==" "!=" "-" "|" "-=" "|=" "||" "<" "<="
+    "*" "^" "*=" "^=" "<-" ">" ">=" "/" "<<" "/=" "<<=" "++" "=" ":=" "%"
+    ">>" "%=" ">>=" "--" "!"  "..."  "&^" "&^=" "~")
+  "Go operators for tree-sitter font-locking.")
+
+(defvar go-ts-mode--font-lock-settings
+  (treesit-font-lock-rules
+   :language 'go
+   :feature 'bracket
+   '((["(" ")" "[" "]" "{" "}"]) @font-lock-bracket-face)
+
+   :language 'go
+   :feature 'comment
+   '((comment) @font-lock-comment-face)
+
+   :language 'go
+   :feature 'constant
+   '([(false) (iota) (nil) (true)] @font-lock-constant-face
+     (const_declaration
+      (const_spec name: (identifier) @font-lock-constant-face)))
+
+   :language 'go
+   :feature 'delimiter
+   '((["," "." ";" ":"]) @font-lock-delimiter-face)
+
+   :language 'go
+   :feature 'function
+   '((call_expression
+      function: (identifier) @font-lock-function-name-face)
+     (call_expression
+      function: (selector_expression
+                 field: (field_identifier) @font-lock-function-name-face))
+     (function_declaration
+      name: (identifier) @font-lock-function-name-face)
+     (method_declaration
+      name: (field_identifier) @font-lock-function-name-face))
+
+   :language 'go
+   :feature 'keyword
+   `([,@go-ts-mode--keywords] @font-lock-keyword-face)
+
+   :language 'go
+   :feature 'label
+   '((label_name) @font-lock-constant-face)
+
+   :language 'go
+   :feature 'number
+   '([(float_literal)
+      (imaginary_literal)
+      (int_literal)] @font-lock-number-face)
+
+   :language 'go
+   :feature 'string
+   '([(interpreted_string_literal)
+      (raw_string_literal)
+      (rune_literal)] @font-lock-string-face)
+
+   :language 'go
+   :feature 'type
+   '([(package_identifier) (type_identifier)] @font-lock-type-face)
+
+   :language 'go
+   :feature 'variable
+   '((identifier) @font-lock-variable-name-face)
+
+   :language 'go
+   :feature 'escape-sequence
+   :override t
+   '((escape_sequence) @font-lock-escape-face)
+
+   :language 'go
+   :feature 'property
+   :override t
+   '((field_identifier) @font-lock-property-face
+     (keyed_element (_ (identifier) @font-lock-property-face)))
+
+   :language 'go
+   :feature 'error
+   :override t
+   '((ERROR) @font-lock-warning-face))
+  "Tree-sitter font-lock settings for `go-ts-mode'.")
+
+(defun go-ts-mode--imenu ()
+  "Return Imenu alist for the current buffer."
+  (let* ((node (treesit-buffer-root-node))
+         (func-tree (treesit-induce-sparse-tree
+                     node "function_declaration" nil 1000))
+         (type-tree (treesit-induce-sparse-tree
+                     node "type_spec" nil 1000))
+         (func-index (go-ts-mode--imenu-1 func-tree))
+         (type-index (go-ts-mode--imenu-1 type-tree)))
+    (append
+     (when func-index `(("Function" . ,func-index)))
+     (when type-index `(("Type" . ,type-index))))))
+
+(defun go-ts-mode--imenu-1 (node)
+  "Helper for `go-ts-mode--imenu'.
+Find string representation for NODE and set marker, then recurse
+the subtrees."
+  (let* ((ts-node (car node))
+         (children (cdr node))
+         (subtrees (mapcan #'go-ts-mode--imenu-1
+                           children))
+         (name (when ts-node
+                 (treesit-node-text
+                  (pcase (treesit-node-type ts-node)
+                    ("function_declaration"
+                     (treesit-node-child-by-field-name ts-node "name"))
+                    ("type_spec"
+                     (treesit-node-child-by-field-name ts-node "name"))))))
+         (marker (when ts-node
+                   (set-marker (make-marker)
+                               (treesit-node-start ts-node)))))
+    (cond
+     ((or (null ts-node) (null name)) subtrees)
+     (subtrees
+      `((,name ,(cons name marker) ,@subtrees)))
+     (t
+      `((,name . ,marker))))))
+
+;;;###autoload
+(add-to-list 'auto-mode-alist '("\\.go\\'" . go-ts-mode))
+
+;;;###autoload
+(define-derived-mode go-ts-mode prog-mode "Go"
+  "Major mode for editing Go, powered by tree-sitter."
+  :group 'go
+  :syntax-table go-ts-mode--syntax-table
+
+  (when (treesit-ready-p 'go)
+    (treesit-parser-create 'go)
+
+    ;; Comments.
+    (setq-local comment-start "// ")
+    (setq-local comment-end "")
+    (setq-local comment-start-skip (rx "//" (* (syntax whitespace))))
+
+    ;; Imenu.
+    (setq-local imenu-create-index-function #'go-ts-mode--imenu)
+    (setq-local which-func-functions nil)
+
+    ;; Indent.
+    (setq-local indent-tabs-mode t
+                treesit-simple-indent-rules go-ts-mode--indent-rules)
+
+    ;; Font-lock.
+    (setq-local treesit-font-lock-settings go-ts-mode--font-lock-settings)
+    (setq-local treesit-font-lock-feature-list
+                '(( comment)
+                  ( keyword string type)
+                  ( constant escape-sequence function label number
+                    property variable)
+                  ( bracket delimiter error operator)))
+
+    (treesit-major-mode-setup)))
+
+;; go.mod support.
+
+(defvar go-mod-ts-mode--syntax-table
+  (let ((table (make-syntax-table)))
+    (modify-syntax-entry ?/   ". 124b" table)
+    (modify-syntax-entry ?\n  "> b"    table)
+    table)
+  "Syntax table for `go-mod-ts-mode'.")
+
+(defvar go-mod-ts-mode--indent-rules
+  `((gomod
+     ((node-is ")") parent-bol 0)
+     ((parent-is "exclude_directive") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "module_directive") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "replace_directive") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "require_directive") parent-bol go-ts-mode-indent-offset)
+     ((parent-is "retract_directive") parent-bol go-ts-mode-indent-offset)
+     ((go-mod-ts-mode--in-directive-p) no-indent go-ts-mode-indent-offset)
+     (no-node no-indent 0)))
+  "Tree-sitter indent rules for `go-mod-ts-mode'.")
+
+(defun go-mod-ts-mode--in-directive-p ()
+  "Return non-nil if inside a directive.
+When entering an empty directive or adding a new entry to one, no node
+will be present meaning none of the indentation rules will match,
+because there is no parent to match against.  This function determines
+what the parent of the node would be if it were a node."
+  (lambda (node _ _ &rest _)
+    (unless (treesit-node-type node)
+      (save-excursion
+        (backward-up-list)
+        (back-to-indentation)
+        (pcase (treesit-node-type (treesit-node-at (point)))
+          ("exclude" t)
+          ("module" t)
+          ("replace" t)
+          ("require" t)
+          ("retract" t))))))
+
+(defvar go-mod-ts-mode--keywords
+  '("exclude" "go" "module" "replace" "require" "retract")
+  "go.mod keywords for tree-sitter font-locking.")
+
+(defvar go-mod-ts-mode--font-lock-settings
+  (treesit-font-lock-rules
+   :language 'gomod
+   :feature 'bracket
+   '((["(" ")"]) @font-lock-bracket-face)
+
+   :language 'gomod
+   :feature 'comment
+   '((comment) @font-lock-comment-face)
+
+   :language 'gomod
+   :feature 'keyword
+   `([,@go-mod-ts-mode--keywords] @font-lock-keyword-face)
+
+   :language 'gomod
+   :feature 'number
+   '([(go_version) (version)] @font-lock-number-face)
+
+   :language 'gomod
+   :feature 'operator
+   '((["=>"]) @font-lock-operator-face)
+
+   :language 'gomod
+   :feature 'error
+   :override t
+   '((ERROR) @font-lock-warning-face))
+  "Tree-sitter font-lock settings for `go-mod-ts-mode'.")
+
+;;;###autoload
+(add-to-list 'auto-mode-alist '("/go\\.mod\\'" . go-mod-ts-mode))
+
+;;;###autoload
+(define-derived-mode go-mod-ts-mode prog-mode "Go Mod"
+  "Major mode for editing go.mod files, powered by tree-sitter."
+  :group 'go
+  :syntax-table go-mod-ts-mode--syntax-table
+
+  (when (treesit-ready-p 'gomod)
+    (treesit-parser-create 'gomod)
+
+    ;; Comments.
+    (setq-local comment-start "// ")
+    (setq-local comment-end "")
+    (setq-local comment-start-skip (rx "//" (* (syntax whitespace))))
+
+    ;; Indent.
+    (setq-local indent-tabs-mode t
+                treesit-simple-indent-rules go-mod-ts-mode--indent-rules)
+
+    ;; Font-lock.
+    (setq-local treesit-font-lock-settings go-mod-ts-mode--font-lock-settings)
+    (setq-local treesit-font-lock-feature-list
+                '((comment)
+                  (keyword)
+                  (number)
+                  (bracket error operator)))
+
+    (treesit-major-mode-setup)))
+
+(provide 'go-ts-mode)
+
+;;; go-ts-mode.el ends here